Thermostatic switch



y 1957 0. M. ROSENBERG ETAL 2,801,315

THERMOSTATIC SWITCH Filed Dec. 28, 1955 IN V ENTO RS.

DAVID M. ROSENBERG WILLIAM B.BLA|R BYWIZ? AT' ORN EY .an adjusting device.

United States Patent THERMOSTATIC SWITCH David M. Rosenberg, Meadville, and William B. Blair, Sandy Lake, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation oi Pennsylvania Application December 28, 1955, Serial No. 555,970

Claims. (Cl. 200-138) This invention relates to a snap acting switch structure, particularly of the type in which the switch elements are supported in stacked relationship, and it has for an object to provide an improved switch structure of this kind.

Further objects of this invention are to improve the performance and life of the contacts, as well as their current interrupting capacity, in a snap acting switch of the type set forth.

A further object of this invention is to keep the cost of a snap acting switch at a minimum by utilizing similar metal blanks for forming diiierent elements of the .switch.

It is a further object of this invention to increase the contact separation resulting from a snap action in a thermostatically actuated and manually resettable snap acting switch.

A snap acting switch made in accordance with this invention includes a pair of relatively movable contacts, one of which is carried on the free end of a snap acting resilient spring arm. An area of this spring arm between its fixed end and the free contact-carrying end is embossed to make the arm a snap acting element. A pair of fiat spring strips are positioned against opposite surfaces of the spring arm to stiffen the latter between the center of the embossed area and the fixed end of the arm. The arm and the two flat strips are clamped together in the switch stack. One of the spring strips is engaged adjacent the center of the embossed area by a movable element of The device adjusts the free ends of the spring strips and the portion of the spring arm that is clamped therebetween to change the point of instability, for each direction of snap action, at which the free contact-carrying end of the arm snaps over center. Increased snap acting movement of the free end of the arm is obtained due to the fact that the portion of the arm between the two spring strips is kept from moving during the snap action.

These and other objects are effected by the invention as will be apparent from the following description and claims taken in connection with the. accompanying drawing, forming a part of this application, in which:

Fig. 1 is a side elevation of a snap acting thermostatic switch, portions being shown in section for clearness;

Fig. 2 is a section taken along the line IIII of Fig. 1; and

Fig. 3 is an exploded view showing the snap acting element of the switch of Fig. l with two spring strips that are positioned on opposite sides thereof.

Referring to Fig. 1, the snap acting thermostatic switch comprises a pair of contacts 11 and 12 supported on the free ends of flat spring arms 13 and 14, respectively. The opposite ends of these arms are fixed in a stack 15 of switch components. The spring arm 13 will move the contact 11 with a snap action to the dotted line position seen in Fig. 1 when the contact 11 is forced upwardly from the full line position of Fig. 1 beyond a critical position of instability of the arm 13. This snap acting movement of the contact 11 will cause it to move out of engagement with the contact 12 on the arm 14.

A thermally responsive member for actuating the switch 10 comprises a bimetallic strip 16 having one end clamped in the stack 15 and extending parallel to the contact carrying spring arm 14. An electrical insulating member 17 is supported on the free end of the bimeta-l and engages the underside of the arm 14, adjacent the contact 12, as seen in Fig. 1. Upon being heated, the bimetal 16 wiil move the :insulating member 17 upwardly and push the lower contact 12 against the contact 11 on the end of the snap acting member 13. When heated to a predetermined temperature, the bimetal 16 will have deflected sufiiciently to cause the contact 12 to push the other contact 11 past a critical point of instability of the snap acting member 13 and the latter will snap contact 11 out of engagement with the contact 12.

The snap acting spring arm 13 has an annular embossed area bumped out of the plane of the strip to render the strip snap acting. The area 20 is concentric with a circular hole 21 located on the longitudinal centerline of the arm :13 between the contact 11 and the fixed end thereof. The hole 21 at the center of this circular concave-convex area 20 reduces the resistance to snap acting movement of the arm 13. In the drawings, the-left end of this strip 13 is secured in the stack of switch parts and the other end that carries the contact may snap to two positions of stability. In one of these positions, the embossed area 20 will extend outwardly on one side of the strip, and in the other stable position it will extend outwardly on the other side.

vA pair of identical spring strips 22 and 23 are positioned on opposite sides of the snap acting member 13 against the faces thereof. Each of these spring elements 22 and 23 has a portion clamped in the switch stack 15 and tapers to a point adjacent the center of the embossed area 20. The pointed ends 24 and 25 of these strips 22 and 23, respectively, terminate opposite the hole 21 in the center of the bumped area 20 to reduce binding between the strips 22 and 23 and the snap acting arm 13. Both of the spring strips 22 and 23 are bent to bias their ends 24 and 25 upwardly, as seen in Fig. 1. The pointed end 24 of the upper strip 22 is engaged near the center of the embossed area 20 by an adjustable element comprising an insulating pin 30 that extends downwardly from a screw 31. The screw 31 is threaded in a central portion of a metal plate 32 which is also supported in the switch stack 15. The lower spring strip 23 presses upwardly against the lower surface of the snap acting arm 13 and the portion of the arm,13 outside the stack 15 and between the two spring strips, including a sector of the annular embossed area 20, is stiiiened to reduce its movement relative the switch stack 15 during snap acting movement of the arm 13. The position of the adjusting screw 31 determines the angular deflection of this relatively rigid or stiiiened portion of the arm 13 with respect to the end thereof clamped in the stack 15.

The spring arm 13 is reduced in width adjacent the fixed end thereof so that it may be more readily deflected by the two spring strips 22 and 23. The angular adjustment of the stiffened portion of the snap acting arm 13, relative the switch stack 15 determines the positions of instability beyond which the contact 11 must move in order to be snapped in opposite directions.

When the contact arm 13 snaps upwardly to the dotted line position of Fig. 1, the arm 13 engages an abutment comprising insulating pin 34 in a movable reset button 35. By pressing the button 35, the snap acting arm may be reset to the full line position of Fig. 1. The button 35 is slidable within a cylindrical member 36 attached to the outer end of the plate 32. The button 35 has a shoulder 37 to limit its upward movement within the cylindrical member 36. When the snap acting member 13 is in the position indicated by full lines in Fig. l, the reset button is biased upwardly by means of a spring arm 38 having a fixed end secured in the switch stack 15. The arm 38, extending between the plate 32 and the snap acting arm 13, has openings through which the adjusting pin and the reset pin extend.

The fixed ends of the bimetal 16, the plate 32 and each of the spring strips 22 and 23 and spring arms 38, 13 and 14 are provided with respective holes through which a tubular rivet 40 extends. The fixed end of the contact carrying spring arms 13 and 14 are electrically insulated from each other and from the rivet 40 in the stack 15 by means of electrically insulating washers. A pair of terminal members 41 and 42 are positioned in the switch stack 15 to make electrical connections to the two arms 13 and 14, respectively. The rivet 40 applies a compressive force to the plate 32 on one end of the stack 15 and to the bimetal 16 on the other end to clamp all of the switch components in fixed relationship.

Each of the spring arms 13, 14 and 38 is formed from a common blank. The arm 14 is identical to arm 13 except that it is not embossed to make it snap acting. The arm 38 is identical to arm 14 except for the addition of a slot in its free end to accommodate the insulating pin 34 in the reset button 35. The arm 38 is also bent to bias its free end toward the reset button 35. The use of common blanks for each of the arms 13, 14 and 38 reduces the cost of the switch assembly.

The spring strips 22 and 23 not only provide means by which the adjusting screw 31 can adjust the critical over-center points for the snap acting arm 13, but they also keep the portion of the snap acting arm 13 that is restrained therebetween substantially immovable so as to increase the displacement of the contact 11 when the arm 13 moves with a snap action. If the snap acting arm 13 were unrestrained, the bumped area would tend to snap outwardly on different sides of the strip when the latter moves to its two stable positions. When unrestrained, the portion of the arm 13 between the center of the bumped area and the switch stack 15 would deflect relative the stack when the arm 13 snaps over-center. By stiffening this portion of the arm between the spring strips 22 and 23 and preventing it from moving relative the switch stack the snap-acting deflection of the outer contact-carrying end of the arm 13 is increased.

During the snap acting movement of the spring arm 13, the snap acting movement of the contact 11 will be in an are having a center of curvature near the center of the bumped area 20, whereas, the angular adjustment of the snap acting arm effected by the screw 31 will be about an axis extending transversely across the strip where its width is reduced adjacent the stack 15.

While We have shown our invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

What is claimed is:

1. A snap acting switch structure comprising a snap acting spring member having a fixed end and a movable end, an electrical contact supported by the movable end .of said member, a second electrical contact positioned in said switch to cooperate with said first mentioned contact, said spring member having a concavo-convex area intermediate its ends to provide two positions of stability of the movable end thereof on opposite sides of a critical over-center position, a pair of stiffening elements on opposite sides of said snap acting member, each element being supported by said structure with a deflectible portion extending along one of the opposed surfaces of said member between its fixed end and the center of said area, an adjusting device engaging the deflectible portion of one of said elements near the center of the concave-convex area, the deflectible portions of said elements being biased towards said adjusting device, said elements stiifening a portion of said snap acting member between the center of said area and the fixed end thereof, said device being adjustable to change the angular position of the stiffened portion of said snap acting member relative the fixed end thereof to change the critical position at which the movable end of said member snaps over center.

2. A switch structure comprising a pair of contacts movable into and out of engagement with each other with a snap action, a spring member having one end fixed in said structure and a movable end supporting one of said contacts, said member being formed with a concavo-convex area between said ends to provide snap'acting movement of the contact thereon to either of two stable positions, a pair of spring strips disposed adjacent opposite sides of said member, each strip being fixed in said structure adjacent the fixed end of the spring member and extending along a surface thereof to the center of the concavo-convex area, an adjustable element engaging one of said strips near the center of said area, said strips being biased toward said element and clamping a portion of the concavo-convex area therebetween to restrict its movement and provide greater snap-acting displacement of the contact carrying end of said member, and an actuating device for moving the contact carrying end of said member in one direction past .a critical point of instability of effect relative snap-acting movement of said contacts, said element being adjustable to move said strips, changing the location of said critical point relative said actuating device.

3. A switch structure comprising a pair of contacts movable into and out of engagement with each other with a snap action, a spring member having one end fixed in said structure and a movable end carrying one of said contacts, said member being formed with a concavo-convex area between said ends to provide snapacting movement of the contact thereon to either of two stable positions, said member having an opening at the center of said area, a pair of spring strips disposed adjacent opposite sides of said member, each strip being fixed in said structure adjacent the fixed end of the spring member and extending along a surface thereof to the center of said opening, an adjustable element engaging one of said strips near the center of the opening, said strips being biased toward said element and clamping a portion of the concavo-convex area therebetween to restrict its movement and provide greater snap-acting displacement of the contact carrying end of said member, and an actuating device for moving the contact carrying end of said member in one direction past a critical point of instability to effect relative snap-acting movement of said contacts, said element being adjustable to move said strips, changing the location of said critical point relative said actuating device.

4. A stack type thermostatic switch structure comprising a flat snap-acting spring arm having a fixed end and a movable end, a second spring arm having a fixed end and a movable end, a contact supported on the movable end of each of said arms, said snap acting arm having a concavo-convex area intermediate the ends thereof, the contact on the snap acting arm being movable with a snap action between two stable positions on opposite sides of a critical position, said contacts being in engagement in one of said stable positions, a resilient strip adjacent each face of said snap acting arm, each of said strips being secured in the switch stack together with the fixed ends of said contact carrying arms, said spring strips extending outwardly from said stack along opposite surfaces of said snap acting arm to the center of said area, an adjustable element supported for engagement with one of said spring strips, said spring strips being biased toward said element, said spring strips stiffening a portion of the concave-convex area therebetween to render the stiffened portion substantially non-defiectible and increase the deflection of said snap acting contact during its snap acting movement, said element being movable to adjust said strips to change the critical position of the snap acting contact, and thermostatic means for moving said other contact in the direction of said snap acting contact to cause the latter to move out of engagement with said other contact with a snap action.

5. A stack type thermostatic switch structure comprising a flat snap-acting spring arm having a fixed end and a movable end, a second spring arm having a fixed end and movable end, a contact supported on the movable end of each of said arms, said snap acting arm having a circular embossed area intermediate the ends thereof, said area having a hole near the center thereof, the contact on the snap acting arm being movable with a snap action between two stable positions on opposite sides of a critical position, said contacts being in engagement in one of said stable positions, a pair of resilient strips adjacent opposite faces of said snap acting arm, each of said strips being secured in the switch stack together with the fixed ends of said contact carrying arms, said spring strips extending outwardly from said stack along opposite surfaces of said snap acting arm and tapering to a point at said hole, an adjusting screw supported by said structure for engagement with one of said spring strips adjacent the center of said area, said spring strips being biased toward said adjusting screw, said spring strips stiffening a sector of the embossed area of the snap acting arm therebetween to render the stiffened portion substantiaiiv non-deflectible during the snap acting movement, said screw being movable to adjust the angular position of said sector relative the switch stack to change the critical position beyond which the snap acting contact moves with a snap action, and thermostatic means for moving the other contact in the direction of said snap acting contact to cause the latter to move past its critical position and out of engagement with said other contact with a snap action.

References Cited in the file of this patent UNITED STATES PATENTS 2,361,202 Hodgkins Oct. 24, 1944 2,692,317 Bletz Oct. 19, 1954 2,741,682 Schwaneke et a1. Apr. 10, 1956 

